1. Field of the Invention
The present invention relates to a paper tray for a printer and more particularly to a paper tray for a printer that has a paper support plate detachably hinged to the printer body adjacent its paper inlet or outlet.
2. Description of the Related Art
Printers are known in which a plate for supporting paper sheets to be fed through the paper inlet in the printer body or supporting paper sheets ejected through the paper outlet in the printer body is pivotally hinged to the printer body adjacent the paper inlet or outlet. By upwardly rotating the paper support plate into a substantially vertical position in which the plate is substantially parallel to the face of the printer body, the printer can be made compact so as to be convenient to store. Downwardly rotating the paper support plate into a substantially horizontal position allows paper sheets to be horizontally stacked on the upper surface of the plate.
Generally, a portion hinged to another member has to bear a heavy load. Therefore, in order to prevent breakage of a hinge portion, various techniques have been proposed. For example, a structure is known in which a hinge portion of an openable and closable door for covering an operation panel at the front side of a VTR is formed with a protrusion to come in contact with a contact surface on the VTR body when the door is opened, so that a load applied when the door is opened is distributed between a bearing and the contact surface in order to prevent the breakage (see, for example, Japanese laid-open patent publication Hei 11-177257). There is also known a structure in which a synthetic resin bearing having a slit is provided at a main unit and a pivot pin is provided at an openable and closable door so that, when an excessive force is applied to the pivot pin, the slit of the bearing allows the bearing itself to change the shape so as to let the pivot pin off the bearing (see, for example, Japanese laid-open patent publication 2000-13045).
In a printer having a paper support plate pivotally hinged to the printer body adjacent its paper inlet or outlet, it is desirable that the paper support plate can be detached from the printer body when a paper jam in the paper inlet or outlet or other trouble occurs. Thus, a structure as described below is often used at the hinge portion.
FIG. 5 shows main parts of the structure. On a printer body adjacent the paper inlet, there is provided a cylindrical protruding shaft 55 having 45-degree inclined flat portions 55a at part of the cylindrical surface. On one end of a paper support plate 57, there is provided a C-shaped hook 56 that has upper and lower arms 56b and 56c to be open toward the outside of the paper support plate. The opening 56d of the C-shaped hook 56 has a width substantially equal to the distance between the flat portions 55a of the protruding shaft 55. By tilting the paper support plate 57 and moving it diagonally downward so that the protruding shaft 55 is inserted into the C-shaped hook 56, the C-shaped hook 56 is rotatably engaged with the protruding shaft 55. To detach the paper support plate 57 from the printer body, the above procedure is reversed. More particularly, the paper support plate 57 is rotated into the tilted position before moved diagonally upward so that the protruding shaft 55 gets out of the opening 56d of the C-shaped hook 56.
The above described hinge structure is desirable as a structure provided at the paper inlet or outlet of a printer for supporting a paper support plate, in that it allows the paper support plate 57 to be easily attached to or detached from the printer body and has the paper support plate 57 rotatable with the C-shaped hook 56 engaged with the protruding shaft 55. However, the structure has a drawback that the C-shaped hook 56 is prone to breakage especially at the lower arm 56c. As a result of various studies, the inventors of the present invention found the following cause of the breakage of the lower arm 56c of the C-shaped hook.
In order to keep the paper support plate 57 in the horizontal position so that paper sheets can be stacked on the upper surface of the plate, the angle of the downward rotation (rotation in a direction A clockwise in FIG. 5) of the paper support plate 57 has to be limited to specified degree. The conventional structure is designed to limit the downward rotation of the paper support plate 57 by the edge 57a of the paper support plate 57 coming in contact with a housing wall 53a of the printer body. However, it has been found that, when the paper support plate 57 is in the horizontal position, the conventional structure causes a large moment to be produced in a direction clockwise in FIG. 5 with the fulcrum V on the contact portion between the edge 57a of the paper support plate 57 and the housing wall 53a of the printer body, and thereby causes a large reaction force R from the protruding shaft 55 to act on the lower arm 56c of the C-shaped hook 56. The reaction force R has a direct action on the lower arm 56c, which may cause downward buckling of the lower arm and thus may result in a crack or breakage S at the base of the lower arm 56c. 
It is possible to form the entire C-shaped hook 56 thicker in order to prevent a breakage of the lower arm 56c. However, it requires increased amount of resin material. Moreover, even though it can prevent a breakage of the lower arm 56c, there is a possibility that an excessive force is applied to another portion, e.g., a portion of the C-shaped hook 56 that is joined to the paper support plate 57, and as a result, the portion is easy to break, because there is no difference in magnitude and direction of the moment produced with the fulcrum V on the contact portion between the edge 57a of the paper support plate 57 and the housing wall 53a of the printer body.